1. Field of the Invention
This invention relates to the use of salts of esters of long-chain fatty alcohols with alpha-sulfofatty acids as corrosion inhibitors.
2. Statement of Related Art
Industrial processes in which metal surfaces, particularly surfaces of iron and iron alloys, come into contact with oils or oil-containing aqueous emulsions under extreme temperature and pressure conditions are hampered by the problem of corrosion of the metal surfaces. Processes of the type in question include, for example, industrial cooling processes, processes for cleaning metal surfaces and processes for machining metal surfaces, such as drilling, cutting, rolling, etc. Although oils or oil-containing emulsions are used in these processes, the effect of water on the metal surface is still a problem. Moreover, the successive corrosion of the metal parts coming into contact with the oils or oil-containing liquids leads to a drastic reduction in the useful life of the associated fabricating machinery and to problems in the subsequent treatment of the metal surface, for example in the application of a corrosion-inhibiting surface layer by phosphating or lacquering.
Accordingly, it has long been known to add corrosion inhibitors to the oil-based liquids coming into contact with the metal surfaces. Numerous compounds and mixtures of various compounds may be used as corrosion inhibitors, both in predominantly oil-containing liquids and in pure oils.
German published patent application No. 11 49 843 describes semiamides of saturated or unsaturated dicarboxylic acids and salts thereof with aliphatic primary amines as additives for fuel oils and lubricating oils. Although additives such as these distinctly improved the prevention of corrosion, they show a very marked tendency towards foaming which is unacceptable in additives of this type.
Alkali or amine salts of sulfonamidocarboxylic acids used as corrosion inhibitors having a good lubricating effect with very little tendency towards foaming are described in U.S. Pat. No. 3,556,9943 and corresponding German published patent application 12 98 672. However, corrosion-inhibiting preparations containing these compounds are attended by the disadvantages that they can only be produced by elaborate processes and that because of their relatively high content of sulfonamide, they occassionally show toxic effects or are at least potentially toxic, thus necessitating continual toxicological tests and monitoring.
Synthetic petroleum sulfonates are known to inhibit corrosion in oil or oil-containing systems, cf. Ullmanns Enzyklopadie der Technischen Chemie, Vol. 18, 4th Edition (1979), pages 1 and 2; and Winnacker, Kuchler "Chemische Technologie", Vol. 4: "Organische Technologie II", 3rd Edition (1972), page 475. However, the disadvantage of this class of compounds is that they are not biodegradable. Therefore, they cannot be used in processes which inevitably involve contact with the environment, because the egression of corrosion-inhibiting preparations containing compounds such as these into waste waters or into the ground could result in almost inestimable ecological damage.